ד"ר אורי מחלב Digital communication- student version Dr. Uri Mahlab

ד"ר אורי מחלב General overview Digital Radio Theory and Implementation -How a Digital Radio Works

ד"ר אורי מחלב Digital Radio Block Diagram CODER MOD UPCONVERTER DOWNCONVERTER DEMOD DECODER

ד"ר אורי מחלב Analog vs. Digital Modulation AM FM PM DIGITAL With digital modulation information is in the phase and amplitude of the signal

ד"ר אורי מחלב The IQ Diagram Vq Vi magnitude phase Q I

ד"ר אורי מחלב Analog Modulation on the IQ diagram Q I B A C D FM PM

ד"ר אורי מחלב BPSK Timing and State Diagram Reference State 1State 0 = 0 deg.= 180 deg. 0 State1 State BPSK Constellation Diagram Q I t

ד"ר אורי מחלב QPSK Modulation Q I Vi Vq 4 Possible States

ד"ר אורי מחלב 16 QAM State Diagram Q I

ד"ר אורי מחלב Symbol Rate: “The rate at which the carrier moves between points in the constellation”

ד"ר אורי מחלבExample: 16 Mb/s 4 Bits A 16 QAM radio has 4 bit per state (or symbol). If the radio operates at 16 Mb/s, then the carrier must change states or 4 million times per second (4 MBaud) SYMBOL RATE = 4MHz

ד"ר אורי מחלב Some Typical Modulation Formats BPSKQPSK8PSK 16QAM64QAM

ד"ר אורי מחלב QPSK Modulator SERIAL TO PARALLEL CONVERTER CARRIER PHASE SHIFT BPFCOMBINER COMBINED VECTOR STATE DIAGRAM BALANCED MODULATION BALANCED MODULATION QUADRATURE DATA STREAM IN-PHASE DATA STREAM f s = f b/2 BINARY NRZ INPUT SIGNAL fbfb SYMBOL RATE: f s = f b/2 I Q I.F 0° 90°

ד"ר אורי מחלב I, Q, Eye diagram and Constellation EYE I Q CONSTELLATION : I Q 1,

ד"ר אורי מחלב QPSK Demodulator BPF Power Splitter Car Rec. Phase Splitter Symbol timing rec.(STR) Parallel to serial converter LPF. Thresh Comp. Thresh Comp. IF Input Phase Demodulation Phase Demodulation Binary NRZ fbfb f b/2 I Q I Q 0° 90°

ד"ר אורי מחלב 16 QAM Modulator Data 2-to-4 level convert 2-to-4 level convert Premod. LPF Premod. LPF Phase split BPFLO L.F. 16 QAM Output 0° 90° Q I I Q Binary NRZ Data

ד"ר אורי מחלב 16 QAM Demodulator BPF CR STR X2 data con blner LPF LOGICLOGIC 4-to-2 level converter of Q channel. Same design as I channel. IF Input I Q 0° 90° 4-Level Signal 4-Level Signal Regeneration Data Out f b LPF

ד"ר אורי מחלב Which waveform requires more bandwidth? A B time

ד"ר אורי מחלב Bandwidth Considerations

ד"ר אורי מחלב Two random data sequence time frequency

ד"ר אורי מחלב Unfiltered Digital Radio Spectrum

ד"ר אורי מחלב An UNFILTERD Radio CODER MOD U/C D/C DEMOD DECODER time frequency Data is easier to recover but signal requires a lot of bandwidth

ד"ר אורי מחלב A FILTERED Radio CODER MOD U/C D/C DEMOD time frequency Signal requires less bandwidth but data is filtered DECODER

ד"ר אורי מחלב Intersymbol Interference

ד"ר אורי מחלב Nyquist Filtering Raised Cosine

ד"ר אורי מחלב Filter Coefficient & Determines Required B.W. Amplitude Response Linear Phase (Flat Group Delay)

ד"ר אורי מחלב The Filtering is Distributed in the Radio CODER MOD UPCONVERTER DOWNCONVERTER DEMOD DECODER

ד"ר אורי מחלבSUMMARY As the modulation complexity increases, the radio becomes more spectrally efficient. However, it also become more susceptible to errors caused by noise and distortions.

ד"ר אורי מחלב TOTAL PROBABILITY OF NOISE AMPLITUDE EXCEEDING THIS THRESHOLD P(x) X

ד"ר אורי מחלב How Error Occur VOLTAGE PROB Received signal with superimposed noise 1 ERROR 0 ERROR0 1 THRESHOLD DECISION NORMAL 1 VALUE NORMAL 0 VALUE BINARY SIGNAL + AMPLTUDE NOISE FDP

ד"ר אורי מחלב Gaussian Distribution P(x) X NEVER RECHS ZEBO PROBABILITY DENSITY FUNCTION 0=RMS VALUE AFTER SUBTRACTING DC COMPONENT

ד"ר אורי מחלב Meaning of Eye diagram Threshold